ConfigurationBuilder haven't definition for AddJson - asp.net-core-2.0

Question

I'm trying to use connection string from my json file by doing next steps
Json file
{
"ConnectionStrings": {
"PlatformDatabase": "Server=xxxx\\SQLEXPRESS;Database=xxxx;Trusted_Connection=True;"
}
}
Access to json
var builder = new ConfigurationBuilder()
.SetBasePath(System.AppContext.BaseDirectory)
.AddJsonFile("appsettings.json",
optional: true,
reloadOnChange: true);
Configuration = builder.Build();
optionsBuilder.UseSqlServer(Configuration.GetConnectionString("PlatformDatabase"));
Error: ConfigurationBuilder does not contain a definition for
AddJsonFile.
Does anyone have this problem before? I tried searching it but all the solution I found doesn't work now (i suppose with version 2).
EDIT
note. I created .Net Core 2.0 console application

Answer 1

The problem was solved by install the nuget package
Microsoft.Extensions.Configuration.Json

Answer 2

You do not need to explicit add appsettings.json in ASP.NET Core 2.
You just need the followings inside Startup.cs -
public Startup(IConfiguration configuration)
{
Configuration = configuration;
}
public IConfiguration Configuration { get; }
public void ConfigureServices(IServiceCollection services)
{
services.AddDbContext<ApplicationDbContext>(options => options.UseSqlServer(
Configuration.GetConnectionString("PlatformDatabase")));
...
services.AddMvc();
}
public void Configure(IApplicationBuilder app, IHostingEnvironment env)
{
...
}
Program.cs
public class Program
{
public static void Main(string[] args)
{
BuildWebHost(args).Run();
}
public static IWebHost BuildWebHost(string[] args) =>
WebHost.CreateDefaultBuilder(args)
.UseStartup<Startup>()
.Build();
}
Another Approach
You register IConfiguration as Singleton in DI container, and then inject it to your DBContext constructor. Then get the connection string inside OnConfiguring method.
public class Startup
{
public Startup(IConfiguration config)
{
_config = config;
}
private IConfiguration _config;
public void ConfigureServices(IServiceCollection services)
{
services.AddSingleton(_config);
services.AddDbContext<YOUR_DB_Context>(ServiceLifetime.Scoped);
...
services.AddMvc();
}
public void Configure(IApplicationBuilder app, IHostingEnvironment env)
{
...
}
}
YOUR_DB_Context.cs
public class YOUR_DB_Context : IdentityDbContext OR DbContext
{
private IConfiguration _config;
public YOUR_DB_Context(DbContextOptions options, IConfiguration config)
: base(options)
{
_config = config;
}
protected override void OnModelCreating(ModelBuilder builder)
{
...
}
protected override void OnConfiguring(DbContextOptionsBuilder optionsBuilder)
{
base.OnConfiguring(optionsBuilder);
optionsBuilder.UseSqlServer(_config["Data:PlatformDatabase"]);
}
}